a) Field of the Invention
This invention relates to a wet treatment method and apparatus effective for use in a fabrication process of semiconductor devices.
b) Description of the Related Art
RIE (reactive ion etching) has long been used in a metallization step for semiconductor devices. In such a step, deposits of a reaction product called, “polymer” or “wall pieces” remains on a surface of an etched substrate. A polymer stripper treatment step has, therefore, been needed to remove the deposits after the etching. Many of chemicals useful in the polymer stripper treatment step have high viscosity and are expensive, and a significant load is required for the treatment of waste water. Such chemicals are, therefore, circulated and reused in many instances. To permit effective handling of a chemical the composition of which tends to vary due to evaporation or the like, the treatment with the chemical as a polymer stripper is widely conducted by suitably supplying the chemical from a circulating tank onto a surface of a substrate only when the treatment is conducted rather than a bath-type treatment that a substrate is dipped in the chemical. To meet requirements for this treatment, a variety of treatment apparatuses have been developed, including single-wafer or batch processing apparatuses and apparatuses equipped with a mechanism for spraying a chemical onto plural substrates while causing the substrates to rotate (or eccentrically rotate) or to revolve U.S. Pat. No. 4,132,567 that issued on Jan. 2, 1979, U.S. Pat. No. 4,682,615 (Ser. No. 626,702 filed on Jul. 2, 1984). and U.S. Pat. No. 4,609,575 (Ser. No. 626,640 filed on Jul. 2, 1984)).
As examples of chemicals effective for the removal of the above-mentioned polymer, solutions containing an amine and ammonium fluoride dissolved as effective components in a solvent called a “semi-aqueous solvent” are used widely. These chemicals often use, as a solvent, an organic solvent in combination with water to reduce dissociation of such effective components because, if these effective components are simply added to water, they ionize or otherwise dissociate and exhibit unduly high reactivity. Accordingly, the solvent employed in such a chemical is a water-containing organic solvent having high viscosity in many instances. The solvent, hence, tends to remain on each substrate subsequent to its treatment with a polymer stripper, thereby giving a rise to a need for rinsing. Therefore, rinsing is often conducted using water.
The rinsing of a substrate subsequent to its treatment with a chemical effective for the removal of the above-mentioned polymer is, however, accompanied by a problem in that mixing of the chemical with water as a rinsing liquid results in a quick increase in etching rate and causes corrosion of metallization patterns and/or interconnections formed on the substrate. According to an investigation by the present inventors, this problem has been ascertained to markedly arise especially in a situation where the chemical is gradually mixed with water. To cope with this problem, it has thus been a rather common, conventional practice that intermediate or provisional rinsing is conducted to wash off the chemical once with a water-soluble solvent, followed by finish rinsing with water. In view of the environment, however, there is an increasing demand toward performing the rinsing with water alone without conducting the intermediate or provisional rinsing with such a solvent. As a result of an investigation on those removed by such rinsing, they have been found to include a polymer in a dissolved form and a polymer lift off and existing as particles (i.e., a residue). Upon rinsing, it is thus essential to achieve efficient dilution of the solvent and at the same time, effective elimination of these particles from the surface of the substrate.
In the conventional art, the etching rate tended to drop as an inorganic chemical was diluted. The conventional art has, therefore, been developed with a view to minimizing the supply flow rates of a polymer stripper chemical and rinsing water as much as possible in order to minimize the consumption of the inorganic chemical. In the conventional art, a polymer stripper chemical and rinsing water are supplied in small amounts in many instances. As their flow rates are low, the post-etching treatment has been conducted in such a way that, as a measure to meet the above-mentioned desire, a substrate under treatment is treated while rotating it at a low speed or the polymer stripper chemical or rinsing water is once caused to stand up on the surface of a substrate at a low rotation speed and the rotation speed of the substrate is then increased to a high speed to promptly spin it off in its entirety.
On the other hand, an increasing number of polymer strippers has been developed with a view to permitting rinsing with water only. Even with such polymer strippers, it is still impossible to completely avoid the above-mentioned increase in etching rate, which takes place upon rinsing. As a consequence, the etching rate is observed to reach a peak in the course of dilution with rinsing water. Even when a chemical permitting rinsing with only water is used as mentioned above, there is still a demand for the development of a solution regarding how to dilute the chemical quickly with only water to such a low concentration as causing no corrosion, in other words, how to achieve the liquid/liquid replacement with a high efficiency. Especially under a situation that metals of different kinds are in contact with each other and galvanic corrosion hence tends to occur, the conventional rinsing method of a substrate surface with water at such a low flow rate as mentioned above has difficulty in completely avoiding corrosion, leading to an outstanding desire for the development of a method which can achieve the liquid/liquid replacement with a high efficiency.
In general, an inefficient rinsing method requires a longer rinsing time and results in a greater consumption of rinsing water. Such an inefficient rinsing method is, therefore, undesired not only from the standpoint of cost but also from the standpoint of influence to the environment. In all wet treatments, it is thus widely required to heighten the efficiency of rinsing.
In rinsing, particles which have been lifted off have to be removed from the surface of a substrate as mentioned above. A polymer stripper such as that described above or its diluted solution, however, does not necessarily have such a pH as causing the particles to electrically repel in the solution from the substrate. In some instances, these particles may be readily adsorbed on the surface of the substrate, thereby making it difficult to remove them. As a method for permitting removal of particles under any pH conditions, it is necessary to apply a physical external force. Toward this direction, wet treatment methods making use of various physical forces have been under investigation in recent years. Use of a physical force such as ultrasonic waves or brushing, for example, can certainly improve the efficiency of particle removal, but on the other hand, the use of such a physical force has been reported to develop another problem in that semiconductor devices are damaged. It is, therefore, desired to develop a method which does not damage semiconductor devices while heightening the efficiency of a liquid/liquid replacement such as between a chemical and rinsing water. This desire is common to every general wet cleaning.